How much N? Illinois project aims to find out

This year's drought did a number on the nitrogen applied to a lot of cornfields. In some places, it's likely there's still a lot of unused nitrogen in the soil while in other spots, it may all be gone. There's not exactly a clear trend with how much N is left heading into winter, so how can you get an idea of where your fields stand?

That's the goal of a new program in Illinois led by University of Illinois Extension corn agronomist Emerson Nafziger. The Illinois Soil Nitrogen Monitoring Project is gleaning data from farmers around the state to get an idea of just how much of the fertilizer is in the field and what conditions will ultimately lead to what's left in the spring.

"Now that soils have cooled down, the nitrogen, mostly in the form of nitrate, that is in fields most likely will stay in the soil until and unless tile lines run, when we can expect some of it to exit in tile drainage water," Nafziger says. "It’s typical for some loss to take place if we have normal precipitation from fall to early spring, but if this winter is dry, some of the nitrogen there now should be available for next year’s crop,” Nafziger explained. We can't know how much will be there in the spring without taking soil samples at that time, preferably close to planting."

Thus far, the project has shown just how much nitrogen uptake depends on moisture. However, although soil moisture is ultimately the deciding factor on how much of applied nitrogen is eventually taken up by growing plants, it's not a clear-cut situation, Nafziger says.

"This shows how complex the nitrogen interactions are in the soil," he says. "In a year such as 2012, there is little nitrogen loss, uptake ends early as the crop stops taking up water, and fall rainfall can produce new flushes of mineralized nitrogen long after crop uptake stops. We think that soil moisture was the main factor determining both yield and the amount of nitrogen in the soil, and that these two factors had independent effects in the tough year that was 2012."

The project will continue through spring, when Nafziger hopes to get a clearer picture of how much nitrogen is remaining and the influence of different combinations of environmental factors, ultimately helping farmers make better early-season fertilizer application decisions.